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Piston Direction - Help!

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Like a dummy :thumbsup:, I did not make note of the direction my piston came out of my bike and I cannot find the "IN" statement on top. Is there any way to tell which way the piston should go in?

Thanks for the help.

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Thanks guys, I needed the help :thumbsup:

Any reason to not use the same piston? Honda shop said it looked to be in great shape with no harmful wear.

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they wear. factory spec is 15 hour replacement on the piston.

Measure, measure measure. Dont worry about how it looks.

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The problem with the piston isnt really wear, its the fact that its got almost no skirt and they get conical from the top down.

JJ is right, its measure measure measure...and not with a caliper either. Gotta use a micrometer.

Its way easier to just buy a new piston. At a minimum, you should hone the cylinder and put a new ring on the old piston though...

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they wear. factory spec is 15 hour replacement on the piston.

15 hours what a joke... my last piston had 150 hours on it and didnt even look too bad when I took it apart.

IMO those factory specs are made to have RIDICULOUSLY low number just so youre buying a whole new engine every month :thumbsup:

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15 hours what a joke... my last piston had 150 hours on it and didnt even look too bad when I took it apart.

IMO those factory specs are made to have RIDICULOUSLY low number just so youre buying a whole new engine every month :thumbsup:

There is a reason for it. The crf450 on the dyno will lose about 5hp around 10hours of use on the motor. So the 15 hour service interval is spot on to keep the motor in peak performance.

can you get more out of it? sure, but you are losing power and also have the chance of failure. most normal people replace pistons at around 50 hours. But never reuse a CRF piston, the skirt is to short and wears.

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There is a reason for it. The crf450 on the dyno will lose about 5hp around 10hours of use on the motor.

do you have proof of that? I kinda find that hard to believe... why would there all of a sudden be a 10% decrease in HP?? 10% is a lot to lose IMO.

is it the piston, or the piston rings that are causing that 10% loss?

but if what you said is true.. I assume only hardcore racers (ie: pros) would do that kid of maintenance, not the average joe trail rider.

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either Eddy or Ron posted that fact up years ago on this board. You can search for that.

why? rings and the short skirt of the piston. It is more like a 125 piston that you need to rering and replace frequently.

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either Eddy or Ron posted that fact up years ago on this board. You can search for that.

why? rings and the short skirt of the piston. It is more like a 125 piston that you need to rering and replace frequently.

hmm, if one of those two posted it than it makes it a lot more believable. I would still like to see the actual dyno sheets if possible, thats very interesting.

on a side note.. im sure the decrease happens gradually, so you wouldnt notice it like its night and day.

I just re-did my engine (cylinder, piston, rings, top end, SS valves) and notice it has a bit more "pep", but the top speed isnt as high (vapor computer) because of the SS valves. maybe its just because im not used to it as I havnt ridden it in 7 months.

I will def keep an eye on it though, it currently has 3 hours on it and I will see if I can feel if it has less power around the 15-20-25 hour mark.

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